(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method that reduces electromagnetic coupling between an inductor created over the surface of a silicon substrate and the underlying silicon substrate.
(2) Description of the Prior Art
Semiconductor devices have of late seen increased use in such applications as cellular telephones, wireless modems and a general range of communication equipment, which has created the need for Integrated Circuits having capabilities of radio frequency (RF) amplification up to extended frequencies in the range of several gigahertz. This has led to the need to create Integrated Circuits whereby active semiconductor elements are combined with passive electrical components and are created over the surface of one monolithic semiconductor substrate.
There are a number of significant advantages in integrating on one semiconductor monolithic substrate the functions of conventional semiconductor devices with functions that are typically performed by a RF amplifier. For instance, manufacturing costs can be significantly reduced while power consumption for the combined functions is also limited. Inductors however typically are of significant size and therefore require a large surface area of the semiconductor device for their implementation. The inductors are typically formed on the surface of a substrate in a spiral form, resulting in parasitic capacitance and substrate loss that have a serious negative effect on the functionality of the created LC circuit by sharply reducing the frequency of resonance of this circuit.
The incorporation of RF inductors without sacrificing device performance due to substrate losses has been extensively researched in recent years. Some of the techniques that have been used for this approach include:
the selective removing (by etching) of the silicon underneath the inductor (using methods of micro-machining)
using multiple layers of metal (such as aluminum) interconnects or of copper damascene interconnects
using a high resistivity silicon substrate
employing biased wells underneath a spiral conductor
inserting various types of patterned ground shields between the spiral inductor and the silicon substrate
increasing the thickness of the inter-layer dielectric.
The above listing of researched alternatives is not meant to be complete or all inconclusive. All of the above approaches have as common objectives to:
1) enhance the quality (Q) value of the inductor, and
2) increase the frequency of the LC self-resonance thereby increasing the frequency range over which the inductor can be used.
The invention addresses the above highlighted concerns an provides a method whereby the electromagnetic coupling between a horizontal inductor, that is created over the surface of a silicon substrate, and the underlying silicon substrate is reduced, thus increasing the operational capability and frequency range of the inductor.
U.S. Pat. No. 6,093,599 (Lee et al.) shows a process for an inductor over a polysilicon filled trench.
U.S. Pat. No. 6,225,182 B1 (Chu et al.) discloses a process for an inductor over an epitaxial layer.
U.S. Pat. No. 6,057,202 (Chen et al.) reveals a spiral inductor process over an air trench in the substrate.
U.S. Pat. No. 6,153,489 (Park et al.) shows an inductor over a porous silicon layer.
A principle objective of the invention is to improve circuit performance of semiconductor devices comprising active and passive components over the surface of one monolithic substrate.
Another objective of the invention is to provide a method for increasing the separation between an inductor that is created over the surface of one monolithic substrate and the underlying monolithic substrate.
Yet another objective of the invention is to improve RF circuit performance for RF circuits that are created using an inductor that is created over the surface of one monolithic substrate.
In accordance with the objectives of the invention a new method is provided for the creation of a horizontal spiral inductor over the surface of a silicon substrate. A first layer of dielectric is deposited over the surface of the substrate, this first layer of dielectric is patterned and etched creation islands of first dielectric material overlying the surface of the substrate, the islands of first dielectric material align with coils of a thereover to be created spiral inductor. The openings created in the layer of dielectric by the patterning and etching of the first layer of dielectric are filled by selective deposition of epitaxial silicon therein. Second and third layers of dielectric are successively deposited over the surface of the first layer of dielectric. A spiral horizontal inductor is then created over the surface of the third layer of dielectric.